Abstract
The purpose of this work was to synthesize and characterize oligoglycerols with the chains of more than four repeating units. Those oligoglycerols may have some interesting applications, among others, as polyoxyalkylation starters. The glycerol oligomerization process was carried out during 12 h, at 230 °C, under the pressure of 0.4 bar, with the use of sodium carbonate as a homogeneous basic catalyst; various concentrations of the catalyst in the reaction medium were used. The reaction products were analyzed with the use of direct infusion electrospray ionization mass spectrometry (ESI-MS), nuclear magnetic resonance (13C NMR) and Fourier transform infrared spectroscopy (FTIR) techniques. Based on the analytical findings, the compositions of the obtained product mixtures and the structures of oligoglycerols present in individual fractions were determined. The effect of catalyst concentration on the composition of the post-reaction mixture was observed. Moreover, in addition to the conventional linear oligomers (α,α-oligoglycerols), two new types of the oligomers were for the first time detected in the post-reaction mixture: one with two hydroxyl groups and the other with a carboxylate group at the α-carbon atom.
Highlights
The presently growing interest in fuels from renewable sources is driven by the efforts of government authorities, which results from the depletion of oil resources
In addition to the conventional linear oligomers (α,α-oligoglycerols), two new types of the oligomers were for the first time detected in the post-reaction mixture: one with two hydroxyl groups and the other with a carboxylate group at the α-carbon atom
The oligomerization experiments demonstrated that the conversion was high in each case for the tested catalyst concentrations in the range of 0.67–3.33 wt %
Summary
The presently growing interest in fuels from renewable sources is driven by the efforts of government authorities, which results from the depletion of oil resources. Oligoglycerols with 2–3 repeating units have many applications in the cosmetic and pharmaceutical industries, while oligomers with four and more repeating units can be used as components for the production of fatty acid esters or as starters for the polyoxyalkylation process. It is a great challenge for scientists to control the glycerol oligomerization process to selectively produce the desirable oligomer or the desirable fraction of oligoglycerols, which can be done principally by selecting the catalyst and its Polymers 2019, 11, 144; doi:10.3390/polym11010144 www.mdpi.com/journal/polymers
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